Fundamentally, it's about whether the university views the applicant as a valuable resource or as a bag of money. At good research programs, professors convene

Fundamentally, it's about whether the university views the applicant as a valuable resource or as a bag of money. At good research programs, professors convene to decide which PhD applicants they want to accept, with the knowledge that the people they accept are going to work with them for years as on their research projects as advisees. To receive an un-funded acceptance means that the consensus of the professors reviewing applications was that covering the applicant's tuition and stipend to have them as an advisee would be a waste of grant money. It's essentially a rejection, because it means nobody actually wanted to be the applicant's advisor. Starting a PhD under those circumstances is just setting yourself up for failure. If a PhD program in science or engineering (or any discipline where professors have a fair amount of grant money to spend) isn't willing to pay you to attend, take that as a rejection and move on. Edit: This is why you generally have to pay to attend a Master's program, but get paid to attend a PhD program. Teaching Master's students is just a waste of time, while teaching PhD students pays off when they become productive research assistants for the remainder of the time it takes them to write a thesis. The pro tip is that if all you want is a Master's degree, you should still apply for a PhD program and then leave with your Masters degree after a year or two.